Flow meters are divided into two categories: liquid and gas. Due to the differences in characteristics between liquids and gases, liquids are usually measured in terms of volume flow, while gases are measured in terms of mass flow. While some volumetric systems can monitor gas flows, totalized flow can cause problems. Therefore, mass-flow sensing technology is usually the best option when measuring air or other gases, especially in crucial applications.
Measurement of the air and other gases in chemical process industries (CPI) production facilities is essential for various reasons, including safety, process control, product quality, production efficiency, environmental compliance, and cost. Major accidents, emergency shutdowns, unplanned maintenance, production slowdowns, and cost overruns are all possible outcomes when measuring inaccurate or unreliable air or other gases.
The use of flow measurement technology in CPI operations is currently limited to the most basic type of measurement: volumetric flow. Only about half of the possible methods for measuring gas flow are suitable for heavy-duty metering applications, and even then, there are other considerations that affect their use. For example, one technology may be more accurate at measuring a specific type of material than another, or it might require more space. In addition, depending on what materials need to be measured and how much accuracy is required, each technology has its advantages and disadvantages.
When choosing a flow meter for gas measurement jobs in CPI plants, the expression “information is power” becomes a key consideration. This is because the same flow-sensing technology selected for one application in a plant may be the wrong choice for another application, even though they are close by. Your choice of flow-sensing technology will determine how well you can monitor those applications.
In the manufacturing industry, measuring the flow of gases and air is vital for a proper product. If the wrong flow meter is selected, the cost of picking it can be in the thousands of dollars. It’s also essential to choose the right type of flow meter for your application.
The cost of failing to perceive minor differences in air and other gas flow measurement systems may be penalized in the event of security incidents, poor product quality, production delays, or difficulties in respecting the environment.
Pros of Vortex Technology
Vortex flow meters offer many advantages to flow measurement, including easy installation with no impulse lines, no moving parts to service or repair, reduced leak potential, and a wide range of lower flow rates. Vortex meters also offer low power consumption, allowing for use in remote areas.
Additionally, Vortex meters are unique in that they can accommodate liquid, gas, steam, and corrosive applications. Vortex flow meters are also able to withstand high process temperatures and pressures.
Vortex flow meters are well suited for various applications across various industries, including oil and gas, refining, chemical and petrochemical, and food and beverage. In addition, vortex flow meters also excel in steam-related applications, including steam injection and steam measurement for district energy systems and industrial plants.
How Does It Work?
Vortex flow meters measure fluid velocity using an operating principle called the von Kármán effect, which states that as the flow passes through a stubby body, a repeating pattern of swirling vortices is generated. In a vortex flow meter, an obstruction in the flow path, often referred to as a shedding bar, serves as a strain. The shedding bar causes the process fluid to separate and form zones of alternating differential pressure called vortices around the back face of the shedding bar.
The vortices cause a small sensing element behind or inside the shedding bar to oscillate at a specific frequency. The velocity of the working fluid is directly proportional to the frequency of the vortices generated by the shedder bar’s unique geometry. The volumetric flow can be calculated with the pipe’s known section. Vortex flow meters often utilize a pressure and temperature sensor to achieve a compensated mass flow measurement.
Common Measurement Applications
Gas flow meters are often required to comply with IEC 61508/61511 (SIL) as part of a Safety Instrumented System in many applications. These systems must be designed and installed per this standard, which requires them to be designed to withstand extreme pressure, shock, and vibration conditions. The following sections cover four typical and complex gas flow measurement applications in chemical facilities.
GAS DISTRIBUTION METERING
Gas distribution meters measure the number of gases in a process stream or system. These meters are also called flow meters and displacement meters. This instrument measures the differential pressure between two points in a stream of gas utilizing a calibrated glass tube or column filled with liquid. The pressure differential causes the liquid to rise within the tube until it reaches its equilibrium with ambient pressure. At this point, it is displaced upward through an outlet valve into an analyzer at a constant rate that depends on flow rates through the meter and volumetric flow rates in both pipes.
FLARING SYSTEM
Flaring systems are necessary for many chemical processes’ safe and efficient operation. They use a variety of gases to move massive amounts of specific gases, such as nitrogen, argon, and oxygen, for inert ions, purging, or blanketing. Other gases, such as hydrogen, would be needed as a catalyst. Accurately measuring these gases is necessary for process control, inventory control, and cost management.
TANK BLANKETING
Tank blanketing is filling a tank with inert gases to displace air or other gases to protect sensitive equipment from corrosive or explosive atmospheres. Most tanks require large volumes of nitrogen, argon, and oxygen to create inert gases that are less reactive than air and allow the tank to be filled safely with liquid chemicals. Some tanks may also require purging by pumping out the inert gas before filling the tank with chemicals.
STACK GAS MONITORING
The stack gas monitoring system (SGMS) is a one-stop shop for environmental compliance. Its components include multiple flow sensors, blowers, and scrubbers, all required to measure plant waste gases’ discharge through huge stacks with scrubber systems. EPA 10 CFR 40 and 40 CFR 98; EUROPEAN UNION. Directives 2003/87/EC and 2007/589/EC.US MMR 30 CFR Part 250, Subpart K, Section 250, and others are among the standards that must be met by Continuous Emission Monitoring Systems (CEMS).
GAS FLOW CHALLENGES
Gas flow measurement is critical for process engineers to maintain accurate fluid flows, which can be affected by pressure drops caused by cross-flow and back-pressure. Gas flow measurement must be accurate, reliable, and repeatable. The ability to measure gas flow accurately requires that the measuring equipment has an accurate flow rate range and resolution for each component in the system.
LOW AND HIGH FLOWS
It’s essential to be aware of low-flow conditions to perform routine maintenance and catch leaks quickly. When the network is malfunctioning, you’ll need a vortex flow meter that can measure high flows and has a wide operating range.
METER CALIBRATION
Vortex flow meters must be calibrated for hydrocarbon composition gases and customized to match the specific process conditions for an accurate reading.
LARGE LINE SIZES
When pipe widths increase, the number of flow meter technologies is reduced. Specific considerations are then needed for selecting a flow meter for longer lines.
AVAILABLE STRAIGHT RUN
All velocity-based flow meter systems necessitate straight-run pipes on both sides of the meter. This is to ensure that a reliable measurement is taken. However, it can be challenging to fit this in busy production or processing environments.
LIMITED ACCESS
Insertion-style meters are often inserted into or retracted from a process using a ball valve, which means that the meter is quickly inserted or retracted. Compared to this type of meter, spool-style flow meters can require lengthy shutdowns and high maintenance costs for removal and insertion.
Conclusion
This article has covered the basics of using a vortex flow meter to measure nitrogen flow. While there are other ways to measure nitrogen flow, the vortex flow meter is one of the most accurate and reliable methods. If you need to measure nitrogen flow for any reason, we hope this article has given you the information you need to get started. Contact sales@instruthink.com, or visit our website at www.instruthink.com to learn more.
